1. Field of the Invention
The present invention relates generally to RFID technology, and particularly to HF-RFID coupler sensor systems operating by transformer action.
2. Technical Background
Casino managers are interested in the capability of recording all of the bets being placed within their premises in real time. This requires a precise and reliable means for identifying the various gaming chips disposed inside, or in close proximity to, the betting zones, as delineated by the markings disposed on the surface of the gaming tables. What is needed is the ability to automatically flag in real-time, or in near rear time, any unusual and suspicious events. A system is also needed that continuously tracking the performance of individual players. This system could also be used to assess the short, medium and long-term performance of casino personnel.
When the objects are gaming chips, tokens, or plaques, and the surface is a casino gaming table such as Baccarat, Mini-baccarat, Blackjack or Pai Gow Poker, the demarked areas of interest are called “betting spots” or areas associated with each player's bet. The table top is delineated with graphics and other indicia on a covering material called a “layout”. In play and placing bets, the chips may be stacked in columns up to 20 high. For Blackjack, allowance must also be made for the placement of “double down” or “split” bets which are placed just outside the “betting spot”. For Baccarat the player betting areas are adjacent and also include adjacent “banker/player/tie” locations.
In one approach, radio frequency identification (RFID) technology has been considered. RFID technology is commonly based on radiated fields (far fields) operating at approved frequencies such as 433 MHz, 915 MHz, 2.4 GHz etc. While promising, this technology has a major drawback. It is not particularly precise in terms of spatial resolution. As a result, its potential is limited to gaming surfaces with single betting areas, such as poker tables, or to tables with betting areas separated by relatively large spaces. Because of both its operating principle and the frequencies at which it operates, this technology is subject to effects that disturb the local field. For example antennas may be detuned by parasitic capacitance (people and metal objects). Signals may be attenuated by the human body. Further, signal propagation may be affected by multi-path phenomena. Accordingly, existing RFID based technology is inadequate when applied to gaming surfaces having multiple betting areas in close proximity to each other, such as the ones used in blackjack or baccarat. The problem is exacerbated when the gaming chips are disposed on the separation lines between betting areas, such as roulette tables.
When automatically communicating with the embedded RFID in each chip responses must be correctly associated with a player location/bet area for this information to be useful to a gaming table system tracking bets and payouts. Accordingly, it is necessary to know the precise location or presence of “tagged objects” within a demarked area. The size covers a few inches of extent and adjacent areas may have contiguous narrow boundaries on the order of ¼ inch. All sensing equipment must be below the table top and out of sight of the players. That is, it is not desired to place couplers, antennas, etc., above the table top.
Thus, some have considered using inductively coupled RFID in the HF frequency band. The terms “Induction field” or “induction coupler” refer to the domain of interacting short range magnetic fields (H fields) that operate by “transformer action” rather than electromagnetic radiation. Magnetic coupling RFID based technology typically operates at approved frequencies in the 125 KHz or 13.56 MHz bands. Because of the inherent “near field” characteristics of this technology, the signal dies off very rapidly beyond the intended coverage area and surrounding environment variations have much less of an impact. In this approach, an RFID inlay, i.e., the “tag,” is disposed within the gaming chip. The inlay is an electronics assembly substrate that connects a planar coupler coil or loop and the semiconductor RFID die. Those of ordinary skill in the art will understand that the term “read,” or “reading chips,” refers to an RFID Reader electronics unit transmitting one or more interrogation messages to the RFID tag disposed within the gaming chip. The interrogation message supplies a wireless “induction field” that provides power to the passive RFID inlay. The class of RFID used is “passive” where tags are powered solely by capturing energy from the Reader-generated impinging field. The RFID inlay receives the interrogation message(s) and provides a response to the reader. These RFID devices also follow the rule of Reader Talks First (RTF).
However, there are drawbacks associated with this approach as well. While the transformer based induction coupler technology represents an improvement over the radiated far-field RFID technology, it is not accurate enough to discriminate between closely spaced betting zones. As noted above, chips may be stacked on top of each other. Any approved system must provide communication with a chip on the top of a stack that may be 25 chips high. The lateral fall-off characteristics of the coupler-generated H field (magnetic field) which can be computed by using the Biot-Savart law. Those of ordinary skill in the art will understand that the magnetic field produced by an embedded loop is roughly spherically shaped. Accordingly, the magnetic field extends approximately the same distance laterally as it does vertically. In particular, the field strength required to reach the top of the chip stack will also result in the field impinging on the neighboring betting spot. This phenomena is commonly referred to as “cross read” or “cross talk.”
What is needed is an induction coupling RFID system that addresses the needs described above. In particular, what is needed is an RFID system that is configured to communicate with each chip in a stack of chips that may include 20-25 chips, while simultaneously preventing cross-read or cross-talk. As such, an RFID reader system having a lateral resolution of at least 0.25 inches is required.